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From: Lew <noone@lewscanon.com>
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Subject: Re: group by hour + distinct
Date: Fri, 26 Nov 2010 11:07:05 -0500
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Michele Petrazzo - Unipex wrote:
> P.s. Have you some references about the "subquery" keyword? I found only
> the word subquery as "use" (for example: select a from b where id in
> (select id from table)), but not as sql [sic] command.

"subquery" is not an SQL keyword.
<http://www.postgresql.org/docs/9.0/interactive/sql-keywords-appendix.html>

Nor is it a command all by itself.

Reading the documentation might help you:
<http://www.postgresql.org/docs/9.0/interactive/queries-table-expressions.html#QUERIES-SUBQUERIES>
<http://www.postgresql.org/docs/9.0/interactive/sql-expressions.html#SQL-SYNTAX-SCALAR-SUBQUERIES>
<http://www.postgresql.org/docs/9.0/interactive/functions-subquery.html>

Or try:
<http://lmgtfy.com/?q=SQL+subquery>

-- 
Lew